A variety of technologies have been developed for transmitting power and or signals (such as data signals from sensors or control signals for controlling devices) to/from deep underground in hydrocarbon production wells. One such technology involves the use of current transformers to induce a current onto the tubing and pick it up again from the tubing. An example of this technology is described in WO2007/004891. Current transformers (as referred to herein) essentially consist of a closed loop of inductive material enclosing the tubing.
Other technologies include using inductive coupling in the use of coupled loop antennas. As referred to hereafter, the term “inductive coupler” refers to any form of construction where a current or magnetic field is induced, and unless indicated otherwise includes current transformers as well as other types of inductive coupling devices. There have also been quite a few attempts at making down-hole wet mate cable connectors, both for electrical and optical connections, but generally so far the results are at best questionable.
Through Tubing Rotary Drilling (TTRD) has become established as a cost-effective method of increasing access to hydrocarbon reserves. Using existing wells in mature reservoirs, additional reserves are accessed through the existing well completion tubing by drilling new sidetracks branching off the existing production tubing. However, well branches such as TTRD branches present considerable problems, particularly for installing signal and power transmission systems. The cables in cable systems are especially vulnerable to damage. Also, the existing current transformer or inductive coupling technologies have a major problem if there is a short circuit between the inside of the tubing and the annulus fluid between the production tubing and the well bore along a long length of transmission. The annulus fluid could typically be a brine containing corrosion inhibitors, but could be diesel or other non-conductive and non-corrosive fluid.
Accordingly, there is a need for an improved way of making a connection to an induced-current (or similar) system for power and/or data signal transmissions in a well branch, where the new completion is not brought back to the surface but is hung off in the production tubing. The same principles may be used both for TTRD branches and in many other well branch constructions.